Curable fluoroelastomer compositions

ABSTRACT

This invention relates to curable fluoroelastomer compositions comprising a) fluoroelastomers having either nitrile, alkyne or azide cure sites and b) fluorinated curatives containing diazide, dinitrile or dialkyne groups for reacting with cure sites on the fluoroelastomer. Fluoroelastomers having azide cure sites form crosslinks with curatives having dinitrile or dialkyne groups. Fluoroelastomers having nitrile or alkyne cure sites form crosslinks with curatives having diazide groups.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 12/486,325 filedJun. 17, 2009.

FIELD OF THE INVENTION

This invention relates to curable fluoroelastomer compositionscomprising fluoroelastomers having either nitrile, alkyne or azide curesites and fluorinated curatives containing diazide, dinitrile ordialkyne groups for reacting with cure sites on the fluoroelastomer.

BACKGROUND OF THE INVENTION

Elastomeric fluoropolymers (i.e. fluoroelastomers) exhibit excellentresistance to the effects of heat, weather, oil, solvents and chemicals.Such materials are commercially available and are most commonly eithercopolymers of vinylidene fluoride (VF₂) with hexafluoropropylene (HFP)or copolymers of VF₂, HFP, and tetrafluoroethylene (TFE).

Other common fluoroelastomers include the copolymers of TFE with one ormore hydrocarbon olefins such as ethylene (E) or propylene (P), and alsothe copolymers of TFE with a perfluoro(alkyl vinyl ether) such asperfluoro(methyl vinyl ether) (PMVE).

Many fluoroelastomers require incorporation of a cure site monomer intotheir polymer chains in order to crosslink efficiently (Logothetis, A.L., Prog. Polym. Sci., Vol. 14, pp 251-296 (1989); A. Taguet et al.Advances in Polymer Science, Vol. 184, pp 127-211 (2005)). Without sucha cure site monomer, the fluoroelastomer may not react at all withcuring agents, it may only partially react, or reaction may be too slowfor use on a commercial scale. Seals made from poorly crosslinkedelastomers often fail sooner than might otherwise be expected.Unfortunately, disadvantages are associated with many of the cure sitemonomers and curatives in use today. For example, some curatives aretoxic. Cure site monomers which contain reactive bromine or iodine atomscan release byproducts during the curing reaction that are harmful tothe environment. Other cure site monomers (e.g. those which containdouble bonds at both ends of the molecule) may be so reactive that theydisrupt polymerization of the fluoroelastomer by altering thepolymerization rate, terminating polymerization, or by causingundesirable chain branching, or even gelation to occur. Lastly,incorporation of a cure site monomer into a fluoroelastomer polymerchain may negatively impact the properties of the fluoroelastomer (bothphysical properties and chemical resistance).

There exists a need in the art for new fluoroelastomer cure systems,both new cure site monomers which are environmentally friendly, do notdisrupt polymerization and which do not detract from the properties ofthe fluoroelastomer, and new curatives for forming crosslinks with curesite monomers.

SUMMARY OF THE INVENTION

An aspect of the present invention is a curable composition comprising

A) a fluoroelastomer comprising copolymerized units of i) a firstmonomer selected from the group consisting of vinylidene fluoride andtetrafluoroethylene and ii) a cure site monomer having a cure siteselected from the group consisting of azide, sulfonyl azide and carbonylazide groups; and

B) a curative having the formula X—(CH₂)_(n)—R—(CH₂)_(m)—X, wherein X isan alkyne group or a nitrile group, n, m are independently 1 to 4, and Ris selected from the group consisting of i) a C₃-C₁₀ fluoroalkylenegroup, ii) a C₃-C₁₀ fluoroalkoxylene group, iii) a substituted arylenegroup, iv) an oligomer comprising copolymerized units of vinylidenefluoride and perfluoro(methyl vinyl ether), v) an oligomer comprisingcopolymerized units of vinylidene fluoride and hexafluoropropylene, vi)an oligomer comprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and vii) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin.

Another aspect of the present invention is a curable compositioncomprising

A) a fluoroelastomer comprising copolymerized units of i) a firstmonomer selected from the group consisting of vinylidene fluoride andtetrafluoroethylene and ii) a cure site monomer having a cure siteselected from the group consisting of nitrile groups, and alkyne groups;and

B) a curative having the formulaN₃(Y)_(p)—(CH₂)_(n)—R—(CH₂)_(m)—(Y)_(p)N₃, wherein Y is SO, SO₂, C₆H₄,or CO, p is 0 or 1, n, m are independently 1 to 4, and R is selectedfrom the group consisting of i) a C₃-C₁₀ fluoroalkylene group, ii) aC₃-C₁₀ fluoroalkoxylene group, iii) a substituted arylene group, iv) anoligomer comprising copolymerized units of vinylidene fluoride andperfluoro(methyl vinyl ether), v) an oligomer comprising copolymerizedunits of vinylidene fluoride and hexafluoropropylene, vi) an oligomercomprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and vii) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to curable fluoroelastomercompositions that are based on new combinations of copolymerized curesite monomers and curing agents.

Fluoroelastomers employed in the curable compositions of the inventiontypically contain between 25 and 70 weight percent, based on the totalweight of the fluoroelastomer, of copolymerized units of a first monomerwhich may be vinylidene fluoride (VF₂), or tetrafluoroethylene (TFE).The fluoroelastomer further comprises 0.2 to 10 (preferably 0.1 to 5)weight percent, based on the total composition of the fluoroelastomer,of copolymerized units of a cure site monomer (hereinafter defined). Theremaining units in the fluoroelastomers are comprised of at least oneadditional copolymerized monomer, different from both said first monomerand said cure site monomer, said additional copolymerized monomerselected from the group consisting of fluoromonomers, hydrocarbonolefins and mixtures thereof. Fluoromonomers include bothfluorine-containing olefins (fluoroolefins) and fluorine-containingvinyl ethers (fluorovinyl ethers).

Fluorine-containing olefins which may be employed in thefluoroelastomers include, but are not limited to vinylidene fluoride(VF₂), hexafluoropropylene (HFP), tetrafluoroethylene (TFE),1,2,3,3,3-pentafluoropropene (1-HPFP), 1,1,3,3,3-pentafluoropropene(2-HPFP), 3,3,3-trifluoropropene; chlorotrifluoroethylene (CTFE) andvinyl fluoride.

Fluorine-containing vinyl ethers that may be employed in thefluoroelastomers include, but are not limited to perfluoro(alkylvinyl)ethers and partially fluorinated vinyl ethers. Perfluoro(alkylvinyl)ethers (PAVE) suitable for use as monomers include those of theformula

CF₂═CFO(R_(f′)O)_(n)(R_(f″)O)_(m)R_(f)  (I)

where R_(f′) and R_(f″) are different linear or branchedperfluoroalkylene groups of 2-6 carbon atoms, m and n are independently0-10, and R_(f) is a perfluoroalkyl group of 1-6 carbon atoms.

A preferred class of perfluoro(alkyl vinyl)ethers includes compositionsof the formula

CF₂═CFO(CF₂CFXO)_(n)R_(f)  (II)

where X is F or CF₃, n is 0-5, and R_(f) is a perfluoroalkyl group of1-6 carbon atoms.

A most preferred class of perfluoro(alkyl vinyl)ethers includes thoseethers wherein n is 0 or 1 and R_(f) contains 1-3 carbon atoms. Examplesof such perfluorinated ethers include perfluoro(methyl vinyl)ether(PMVE), perfluoro(ethyl vinyl ether) (PEVE) and perfluoro(propylvinyl)ether (PPVE). Other useful monomers include compounds of theformula

CF₂═CFO[(CF₂)_(m)CF₂CFZO]_(n)R_(f)  (III)

where R_(f) is a perfluoroalkyl group having 1-6 carbon atoms, m=0 or 1,n=0-5, and Z=F or CF₃. Preferred members of this class are those inwhich R_(f) is C₃F₇, m=0, and n=1.

Additional perfluoro(alkyl vinyl)ether monomers include compounds of theformula

CF₂═CFO[(CF₂CF{CF₃}O)_(n)(CF₂CF₂CF₂O)_(m)(CF₂)_(p)]C_(x)F_(2x+1)  (IV)

where m and n independently=0-10, p=0-3, and x=1-5. Preferred members ofthis class include compounds where n=0-1, m=0-1, and x=1.

Other examples of useful perfluoro(alkyl vinyl ethers) include

CF₂═CFOCF₂CF(CF₃)O(CF₂O)_(m)C_(n)F_(2n+1)  (V)

where n=1-5, m=1-3, and where, preferably, n=1.

If copolymerized units of PAVE are present in the fluoroelastomersemployed in the invention, the PAVE content generally ranges from 25 to65 weight percent, based on the total weight of the fluoroelastomer. Ifperfluoro(methyl vinyl)ether is used, then the fluoroelastomerpreferably contains between 30 and 65 wt. % copolymerized PMVE units.

Hydrocarbon olefins useful in the fluoroelastomers employed in thisinvention include, but are not limited to ethylene (E) and propylene(P). If copolymerized units of a hydrocarbon olefin are present in thefluoroelastomers, hydrocarbon olefin content is generally 4 to 30 weightpercent.

Specific examples of fluoroelastomers that may be employed in thisinvention (cure site monomers omitted for clarity) include, but are notlimited to copolymerized units of TFE/PMVE, VF₂/PMVE, VF₂/TFE/PMVE,TFE/PMVE/E, TFE/P and TFE/P/VF₂.

Cure site monomers that may be employed in the fluoroelastomers arethose having nitrile, alkyne or azide groups which will serve asreactive sites to form crosslinks with a curing agent.

Useful nitrile-containing cure site monomers include those of theformulas shown below.

CF₂═CF—O(CF₂)_(n)—CN  (VI)

where n=2-12, preferably 2-6;

CF₂═CF—O[CF₂—CF(CF₃)—O]_(n)—CF₂—CF(CF₃)—CN  (VII)

where n=0-4, preferably 0-2;

CF₂═CF—[OCF₂CF(CF₃)]_(x)—O—(CF₂)_(n)—CN  (VIII)

where x=1-2, and n=1-4; and

CF₂═CF—O—(CF₂)_(n)—O—CF(CF₃)CN  (IX)

where n=2-4. Those of formula (VIII) are preferred. Especially preferredcure site monomers are perfluorinated polyethers having a nitrile groupand a trifluorovinyl ether group. A most preferred cure site monomer is

CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN  (X)

Cure site monomers that contain azide groups include those containingsulfonyl azide or carbonyl azide groups. Examples of sulfonyl azide curesite monomers include, but are not limited toCF₂═CFOCF₂CF(CF₃)OCF₂CF₂—SO₂N₃; CF₂═CFOCF₂CF₂—SO₂N₃;CF₂═CFOCF₂CF₂CF₂—SO₂N₃; and CF₂═CFOCF₂CF₂CF₂CF₂—SO₂N₃ as disclosed inU.S. Pat. No. 6,365,693 B1. An example of a carbonyl azide cures sitemonomer is CF₂═CFOCF₂CF(CF₃)OCF₂CF₂—CON₃ (hereinafter EVE-CON₃). Thelatter may be synthesized by the following reactions starting fromClCF₂—CFCl—O—CF₂CF(CF₃)—OCF₂CF₂—COOH (hereinafter Cl₂-EVE-COOH).

Cl₂-EVE-COOH+PCl₅→Cl₂-EVE-COCl

Cl₂-EVE-COCl+HN₃/Pyridine (or NaN₃)→Cl₂-EVE-CON₃

Cl₂-EVE-CON₃+Zn→EVE-CON₃+ZnCl₂

Examples of cure site monomers that contain alkyne groups include, butare not limited to CF₂═CFOCF₂CF(CF₃)OCF₂CF₂—C≡CH;CF₂═CFOCF₂CF(CF₃)OCF₂CF₂—COOCH₂C≡CH; andCF₂═CFOCF₂CF(CF₃)OCF₂CF₂—CH₂CH₂—O—CH₂C≡CH. A synthesis forCF₂═CFOCF₂CF(CF₃)OCF₂CF₂—C≡CH (hereinafter EVE-C≡CH) from Cl₂-EVE-COOHis below.

Cl₂-EVE-COOH+PCl₅→Cl₂-EVE-COCl

Cl₂-EVE-COCl+KI/Heat→Cl₂-EVE-I

Cl₂-EVE-I+CH₂═CH₂→Cl₂-EVE-CH₂CH₂—I

Cl₂-EVE-CH₂CH₂—I+KOH→Cl₂-EVE-CH═CH₂

Cl₂-EVE-CH═CH₂+Br₂→Cl₂-EVE-CHBr—CH₂Br

Cl₂-EVE-CHBr—CH₂Br+KOH→Cl₂-EVE-C≡CH

Cl₂-EVE-C≡CH+Zn→EVE-C≡CH+ZnCl₂

Likewise CF₂═CFOCF₂CF(CF₃)OCF₂CF₂—COOCH₂C≡CH (hereinafterEVE-COOCH₂C≡CH) may be synthesized via

Cl₂-EVE-COCl+HOCH₂C≡CH→Cl₂-EVE-COOCH₂C≡CH+Zn→EVE-COOCH₂C≡CH

CF₂═CFOCF₂CF(CF₃)OCF₂CF₂—CH₂CH₂—O—CH₂C≡CH (hereinafterEVE-CH₂CH₂—O—CH₂C≡CH) may be synthesized via

Cl₂-EVE-CH₂CH₂—I+HOCH₂C≡CH+Base→Cl₂-EVE-CH₂CH₂—O—CH₂C≡CH+Zn→EVE-CH₂CH₂—O—CH₂C≡CH

Fluoroelastomers employed in the invention may be made by a solution,suspension or emulsion polymerization process. Such processes are wellknown in the art. Preferably, an emulsion process is employed wherein aninorganic peroxide (e.g. sodium or ammonium persulfate) is theinitiator. Optionally a surfactant, particularly a fluorosurfactant maybe included in order to improve the stability of the emulsion.

When the fluoroelastomer contains a cure site monomer having azidegroups, the curatives that may be employed in the compositions of theinvention are those of formula X—(CH₂)_(n)—R—(CH₂)_(m)—X, wherein X isan alkyne group or a nitrile group, n and m are independently 1 to 4,and R is selected from the group consisting of i) a C₃-C₁₀fluoroalkylene group, ii) a C₃-C₁₀ fluoroalkoxylene group, iii) asubstituted arylene group, iv) an oligomer comprising copolymerizedunits of vinylidene fluoride and perfluoro(methyl vinyl ether), v) anoligomer comprising copolymerized units of vinylidene fluoride andhexafluoropropylene, vi) an oligomer comprising copolymerized units oftetrafluoroethylene and perfluoro(methyl vinyl ether), and vii) anoligomer comprising copolymerized units of tetrafluoroethylene and ahydrocarbon olefin. Hydrocarbon olefins that may be employed includeethylene and propylene. These oligomers (i.e. low molecular weightcopolymers) may be prepared according to the processes disclosed in U.S.20090105435 A1. Such oligomers preferably contain 10 to 50 mole percentperfluoro(methyl vinyl ether). The oligomers have a number averagemolecular weight of 1000 to 25,000, preferably 1200 to 12,000, mostpreferably 1500 to 5000.

Specific examples of such curing agents include, but are not limited toNC—(CF₂)_(n)—CN (n=2-20), see U.S. Pat. No. 2,515,246 and Journal ofIndustrial and Engineering Chemistry (Washington, D.C.) (1947), 39,415-17; and H C≡C—(CF₂)_(n)—C≡CH (n=2-20), see K. Baum, et al., J. Org.Chem., 47, 2251 (1982).

When the fluoroelastomer contains a cure site monomer having nitrile oralkyne groups, the curatives that may be employed in the compositions ofthe invention are those of formulaN₃(Y)_(p)—(CH₂)_(n)—R—(CH₂)_(m)—(Y)_(p)N₃, wherein Y is SO, SO₂, C₆H₄,or CO, p is 0 or 1, n and m are independently 1 to 4, and R is selectedfrom the group consisting of i) a C₃-C₁₀ fluoroalkylene group, ii) aC₃-C₁₀ fluoroalkoxylene group, iii) a substituted arylene group, iv) anoligomer comprising copolymerized units of vinylidene fluoride andperfluoro(methyl vinyl ether), v) an oligomer comprising copolymerizedunits of vinylidene fluoride and hexafluoropropylene, vi) an oligomercomprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and vii) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin.

Specific examples of such curing agents include, but are not limited toN₃CH₂CH₂CF₂CF₂CF₂CF₂CF₂CF₂CH₂CH₂N₃; N₃—CH₂CH₂—(CF₂)₄—CH₂CH₂ N₃ (U.S.Pat. No. 4,020,176); N₃—CO—CH₂—(CF₂)₄—CH₂—CO—N₃ (JP 57108055 A); andN₃C₂H₄-poly(VF₂-co-PMVE)-C₂H₄N₃. The latter may be prepared by thereaction of sodium azide with I—CH₂CH₂—(VF₂-co-PMVE)-CH₂CH₂—I madeaccording to the process of US 20090105435 A1.

Curable compositions of the invention may also, optionally, containadditives typically employed in the elastomer industry including, butnot limited to accelerators, acid acceptors, fillers, colorants, processaids, etc.

EXAMPLES Test Methods Nuclear Magnetic Resonance Spectroscopy:

Compositions and the structures were determined by ¹⁹F and ¹H NMRspectroscopy. The NMR spectra were recorded on BRUKER® AC 250 or 400(250 and 400 MHz) instruments, using deuterated acetone as the solventand tetramethylsilane (TMS) or CFCl₃ as the references for ¹H (or ¹⁹F)nuclei. Coupling constants and chemical shifts are given in Hz and ppm,respectively. The experimental conditions for ¹H (or ¹⁹F) NMR spectrawere the following: flip angle 90° (or 30°), acquisition time 4.5 s (or0.7 s), pulse delay 2 s (or 5 s), number of scans 128 (or 512), and apulse width of 5 μs for ¹⁹F NMR.

Chromatography:

Size Exclusion Chromatography (SEC) analysis was performed with aSpectra-Physics apparatus equipped with two PLgel 5 μm Mixed-C columnsfrom Polymer Laboratories and a Spectra Physics SP8430 RI detector.Tetrahydrofuran (THF) was the eluent, temperature was 30° C., and theflow rate was 0.8 mL min⁻¹. Poly(styrene) or poly(methylmethacrylate)standards (Polymer Laboratories) were used to give relative values ofthe molecular weights. Samples of a known concentration (ca. 2 wt. %)were filtered through a 200 micron PTFE chromafil membrane prior toinjection.

Thermal Properties:

The glass transition temperatures (T_(g)) were determined bydifferential scanning calorimetry (DSC) using a Perkin Elmer Pyris 1apparatus calibrated with indium and n-decane. The samples (about 10 mg)were initially cooled to −105° C. for 10 mins, then heated from −100° to50° C. at a heating rate of 20° C./min (a second recooling was done to

−105° C., and the same cycle repeated three times). The values of T_(g)reported herein correspond to the inflection point of the differentialheat flow.

TGA analyses were performed using a Texas Instrument ATG 51-133apparatus under air at the heating rate of 20° C./min from roomtemperature (approximately 20° C.) up to 550° C.

Example 1

In this example, a curable composition of the invention is madecomprising a) a fluoroelastomer terpolymer of vinylidene fluoride (VF₂),perfluoro(methyl vinyl ether) (PMVE) and CF₂═CFOCF₂CF(CF₃)OCF₂CF₂CN(8-CNVE) and b) a diazido curative. The resulting composition is thencured.

(A) Synthesis of the Fluoroelastomer:

A 300-mL Hastelloy autoclave, equipped with inlet and outlet valves, amanometer and a rupture disc, was degassed and pressurized with 30 barof nitrogen to check for leaks. Then, a 0.5 mm Hg vacuum was operatedfor 5 minutes (min.) and subsequently an Ar atmosphere was applied. Thisautoclave degassing procedure was repeated five times. Under vacuum, 8.1g (17.8 mmol) of 1,4-diiodoperfluorobutane, 0.3 g (1.26 mmol) of Na₂S₂O₈dissolved in 90 ml of water, 7.8 g (20 mmol) of 8-CNVE and 1.35 g ofammonium perfluorooctanoate (3.13 mmol) dissolved in 5 ml of1,1,1,3,3-pentafluorobutane were transferred into the autoclave. Then,by double weighing, 16 g (0.25 moles) of VF₂ and 24 g (0.145 mol) ofPMVE were introduced into the autoclave. Then, the autoclave wasprogressively heated to 80° C. During the reaction, the pressure droppedfrom 22 to 14 bars in 24 hours. After reaction, the autoclave was placedin an ice bath for about 60 minutes and 25 g of unreacted PMVE and VF₂was slowly released. The conversion of gases was 38%. After opening theautoclave, 150 ml of butanone was added and the organic layer wasseparated in a separating funnel, was dried over MgSO₄ and filteredthrough sintered glass (G4). The organic solvent was removed by arotating vacuum evaporator at (40° C./20 mm Hg). The resulting yellowviscous liquid was dried at 40° C. and 0.01 mbar vacuum to constantweight. The product (yield 56%) was analyzed by ¹H and ¹⁹F NMRspectroscopy.

(B) Synthesis of the Diazido Curing Agent:

The batch bismonoaddition of α,ω-diiodoperfluorohexane onto ethylene wasperformed in a 160 mL Hastelloy autoclave Parr System, equipped with amanometer, a rupture disk, inlet and outlet valves, and a mechanicalanchor. An electronic device regulated and controlled both the stirringand the heating of the autoclave. The autoclave was left closed for 20min. and purged with 30 bars of nitrogen pressure to prevent anyleakage, and degassed afterwards. Then, a 2 mm Hg vacuum was operatedfor 15 min. The initiator di-4-tert-butylcyclohexyl peroxydicarbonate(4.22 g, 10 mmol) and 30.13 g (54.2 mmol) of I—C₆F₁₂—I in drytert-butanol (40 mL) were introduced via a funnel tightly connected tothe introduction valve. Next, ethylene (4.0 g, 0.14 mol) was introducedby double weighing. The autoclave was then heated up to 50° C. for 7hours. After reaction, the autoclave was cooled to room temperature andthen put into an ice bath. After degassing the unreacted monomer, theautoclave was opened. Tert-butanol was evaporated; the monomer wassolubilized in THF and precipitated from cold pentane. The fluorinateddiiodo product was filtered, washed, and dried at room temperature undera 20 mm Hg vacuum for 24 hours. The yield was 80%. FT-IR: 1138 cm⁻¹(v_(C-F))

¹H-NMR (δ CDCl₃) α: 3.2 ppm (t, ³J_(HH)=7.01 Hz, 4H); β: 2.6 ppm (m,4H);

¹⁹F-NMR (δ CDCl₃) g: −115.2 ppm (m, 4F); h: −121.8 ppm (m, 4F); i:−123.8 ppm (m, 4F).

A mixture composed of 7.80 g (12.8 mmol) of the above-prepared1,10-diiodo-1H,1H,2H,2H,9H,9H,10H,10H-perfluorodecane and 2.21 g (30.8mmol) sodium azide dissolved in DMSO (25 mL) and water (1 mL) wasstirred at 50° C. for 48 hours. Then, the reaction mixture was pouredinto water and was extracted with diethyl ether. This procedure wasrepeated twice. The organic layer was washed with water twice, then with10% sodium sulfite solution twice, water again (3 times) and then brine,dried over MgSO₄ and filtered. Solvent was evaporated under reducedpressure to give 5.0 g of a pale green oil. The yield of the fluorinateddiazide was 94%.

FT IR: 2100 cm⁻¹ (v_(N3)); 1138 cm⁻¹ (v_(C-F))

¹H NMR (δ CDCl₃) α: 3.55 ppm (t, ³J_(HH)=7.07 Hz, 4H), β: 2.30 ppm (m,4H)

¹⁹F NMR (δ CDCl₃) g: −114.2 ppm (m, 4F); h: −121.8 ppm (m, 4F); i:−123.8 ppm (m, 4F)

A curable composition of the invention is made by dissolving 5 g of theabove-prepared VF₂/PMVE/8-CNVE fluoroelastomer in FC-75 solvent(available from 3M) and then mixed with 0.4 g of the telechelic1,10-diazido-1H,1H,2H,2H,9H,9H,10H,10H-perfluorodecane curing agentprepared above. This curable composition is mixed until a clear,transparent and homogenous solution is obtained. The curable compositionis then cast into a mold, resulting in a film. The film is cured at 150°C. for 14 to 20 hours.

Example 2

A curable composition of the invention was made by dissolving 5 g of aTFE/PMVE/8-CNVE fluoroelastomer (prepared substantially as disclosed inU.S. Pat. No. 5,789,489 and containing about 64-67 mol % TFE, 32-34 mol% PMVE and 0.7-1.2 mol % 8-CNVE) in FC-75 solvent (available from 3M)and then mixed with 0.4 g of the telechelic1,10-diazido-1H,1H,2H,2H,9H,9H,10H,10H-perfluorodecane curing agentprepared above, and 0.5 g of zinc chloride. This curable composition wasmixed until a clear, transparent and homogenous solution was obtained.The curable composition was then cast into a mold, resulting in a film.The film was cured at 150° C. for 14 to 20 hours. The resultingcrosslinked fluoroelastomer composition was insoluble in FC-75, whereasthe uncured composition had been soluble in FC-75. TGA showed that T10%was 442° C., while it was 424° C. for uncured fluoroelastomer.

A crosslinking mechanism is shown below wherein azide groups on thecurative react with pendant nitrile groups on the fluoroelastomer toform crosslinks through tetrazole rings.

1. A curable composition comprising A) a fluoroelastomer comprisingcopolymerized units of i) a first monomer selected from the groupconsisting of vinylidene fluoride and tetrafluoroethylene and ii) a curesite monomer having a cure site selected from the group consisting ofazide, sulfonyl azide and carbonyl azide groups; and B) a curativehaving the formula X—(CH₂)_(n)—R—(CH₂)_(m)—X, wherein X is an alkynegroup or a nitrile group, n, m are independently 1 to 4, and R isselected from the group consisting of i) a C₃-C₁₀ fluoroalkylene group,ii) a C₃-C₁₀ fluoroalkoxylene group, iii) a substituted arylene group,iv) an oligomer comprising copolymerized units of vinylidene fluorideand perfluoro(methyl vinyl ether), v) an oligomer comprisingcopolymerized units of vinylidene fluoride and hexafluoropropylene, vi)an oligomer comprising copolymerized units of tetrafluoroethylene andperfluoro(methyl vinyl ether), and vii) an oligomer comprisingcopolymerized units of tetrafluoroethylene and a hydrocarbon olefin. 2.A curable composition of claim 1 wherein said cure site monomer is asulfonyl azide selected from the group consisting ofCF₂═CFOCF₂CF(CF₃)OCF₂CF₂—SO₂N₃; CF₂═CFOCF₂CF₂—SO₂N₃;CF₂═CFOCF₂CF₂CF₂—SO₂N₃; and CF₂═CFOCF₂CF₂CF₂CF₂—SO₂N₃.
 3. A curablecomposition of claim 1 wherein said cure site monomer isCF₂═CFOCF₂CF(CF₃)OCF₂CF₂—CON₃.
 4. A curable composition of claim 1wherein said fluoroelastomer further comprises copolymerized units of atleast one additional monomer, different from said first monomer and saidcure site monomer, wherein said additional monomer is selected from thegroup consisting of fluorine-containing olefins, fluorine-containingvinyl ethers and hydrocarbon olefins.
 5. A curable composition of claim4 wherein said additional monomer is a fluoroolefin selected from thegroup consisting of vinylidene fluoride; hexafluoropropylene;tetrafluoroethylene; 1,2,3,3,3-pentafluoropropene;1,1,3,3,3-pentafluoropropene; 3,3,3-trifluoropropene;chlorotrifluoroethylene and vinyl fluoride.
 6. A curable composition ofclaim 4 wherein said additional monomer is a perfluoro(alkyl vinylether).
 7. A curable composition of claim 1 wherein said curative isselected from the group consisting of NC—(CF₂)_(n)—CN andHC≡—(CF₂)_(n)—C≡CH wherein n is an integer between 2 and 20.